Ultrasonic Material Removal System For Cardiopulmonary Bypass and Other Applications

ABSTRACT

Devices, systems, and methods manipulate target materials within fluids, and may be useful for removing microbubbles and other materials from blood. Ultrasound or acoustic filtering waves may be directed across a flow of blood, and differences in density between the target microbubbles and the blood may enhance separation by driving the lighter matter upward for removal from the blood stream. A disposable acoustically transmissive conduit can replaceably engage an ultrasound transmitter to facilitate sterilization. Exemplary conduits have elongate lumen cross-sections and an axial path resembling a portion of a Mobius strip.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a Divisional of U.S. Ser. No. 11/463,121filed Aug. 8, 2006 (Allowed), which application claims the benefit ofU.S. 60/711,386 filed Aug. 26, 2005; the full disclosures, each of whichare incorporated herein by reference in their entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

NOT APPLICABLE

BACKGROUND OF THE INVENTION

The present invention is generally related to devices, systems, andmethods for manipulating materials within and/or separating materialsfrom fluids. In exemplary embodiments, the invention provides anacoustic or ultrasound filter for removal of microbubbles or othertarget matter from a fluid, particularly for target matter havingacoustic impedances and/or densities which are significantly differentthan that of the remaining fluid. Separation of microbubbles and othermatter from biological fluids can be (for example) beneficial forremoving microbubbles from blood before introduction of the filteredblood into the patient during cardiopulmonary bypass systems, when usingcell-saver systems that filter and return blood that might otherwise belost during surgery, for dialysis treatment, and the like.

A number of different types of treatments rely on external processing ofthe blood of a patient. An example of external blood processing is oftenincluded in heart surgeries that involve cardioplegia, in which beatingof the heart is temporarily halted. During cardioplegia, pumping of theblood through the vascular system, and re-oxygenating the blood can beperformed outside the patient's body by a heart-lung machine of acardiopulmonary bypass system. While the patient is relying on thecardiopulmonary bypass system, the blood flows in a continuous streamfrom the patient, through the heart-lung machine, and back into thepatient. Similarly, patients with compromised kidney function rely ondialysis treatments in which the blood flows from the patient, throughthe dialysis machine, and back into the patient.

In general, biological fluids that are to be introduced into a patientare handled and processed with great care. This can be relativelychallenging during dialysis treatments, cardiopulmonary bypass, andother procedures in which a stream of fluids are removed from the body,processed outside the body, and reintroduced into the body. Suchtreatments often involve filtration, gas exchange, and the like, withthe biological fluid passing through pumps, tubing, filter media, andother artificial structures. Bubbles of various sizes can be introducedinto the biological fluids by this processing. While removal of largerbubbles can be relatively straightforward, it can be quite challengingto effectively remove microbubbles from blood and other biologicalfluids prior to introduction into a patient. Small particulates (andother undesirable materials that are difficult to remove) may also beinadvertently introduced into blood during processing.

While a variety of techniques have been proposed and/or implemented forremoval of microbubbles and other impurities from blood and otherbiological fluids, many known filtration techniques have generally beenfound to be less than ideal. Hence, it would generally be desirable toprovide improved devices, systems, and methods for manipulation and/orseparation of target materials from within fluids, particularly frombiological fluids. It would be particularly desirable if these improvedtechniques were compatible with existing biological fluid processing oreven facilitated improved biological fluid processing to enhance thesafety and efficacy of dialysis treatments, heart-lung machines, and thelike. Ideally, such improved techniques would not significantly increasethe complexity or cost of the existing blood (and other biologicalfluid) processing systems, nor increase the difficulty in sterilizingbiological fluid processing systems.

BRIEF SUMMARY OF THE INVENTION

The present invention generally provides improved devices, systems, andmethods for manipulating target materials within and/or separatingtarget materials from fluids, particularly from biological fluids.Embodiments of the invention may be useful for removing microbubbles andother acoustically manipulatable (and often embolizable) materials fromblood, particularly for treatments involving cardiopulmonary bypass,dialysis treatments, and the like. When used for filtration of blood orother biological fluids, embodiments of the invention may benefit from amismatch of acoustic impedance between the (and from differences indensity between) the target matter (such as microbubbles, microspheres,microbeads, or the like) and the remaining biological fluids, withexemplary embodiments employing waves of acoustic or ultrasound energysweeping upward across a stream of the biological fluid so that acousticfiltering and gravity together drive a lighter target matter upward foreasy removal from the fluid stream. A disposable conduit that is atleast in part acoustically transmissive can acoustically couple thefluid stream to an ultrasound transmitter, facilitating sterilization ofthe system by replacement of the conduit. An exemplary laminar-flowconduit has an elongate cross-section, ideally with a height (in theupward direction traveled by the propagating waves) which issignificantly greater than a width across the conduit. Deleteriousreflection of the waves can be inhibited by a sufficient match betweenthe acoustic impedance of the conduit material opposite the transducerand the biological fluid, by controlling the angle at which the wavesfrom the biological fluid impinge on the conduit material, and the like.An exemplary conduit in which filtration takes place has a pathresembling a portion of a Mobius strip, providing a balanced flowresistance across the conduit lumen and allowing removal of the targetmatter from an at least local maximum height within the lumen.

In a first aspect, the invention provides a filter for separating atarget matter from a fluid flow. The filter comprises a fluid conduithaving an input for receiving the fluid flow, an output, and a lumendefining a fluid flow path from the input to the output. An ultrasoundor acoustic transmitter can generate ultrasound or acoustic waves. Atarget matter port is in fluid communication with the conduit lumen. Thetransmitter is oriented so that the waves drive the target matter acrossthe fluid flow path toward the port.

In many embodiments, the fluid flow at the input will include the targetmatter and a biological fluid. The target matter will often be lessdense than the fluid, and the transmitter can be disposed below thefluid flow path. The port may open to the lumen from above the fluidflow path, allowing the less dense target matter to be removed from thetop of the biological fluid so that gravity aids in separation andremoval of the target matter.

The fluid conduit can have an upper surface which, in the directionalong the fluid flow path, slopes upward toward the port. After passingthe port, the upper surface may then slope downward away from the port.Hence, gravity may further tend to urge microbubbles and other lowdensity target matter upstream and/or downstream toward the port.Regardless of the orientation, an elongate lumen cross-section mayextending in the direction of the wave propagation may enhance filterefficiency and/or effectiveness.

The fluid path resistance across the lumen can be balanced to facilitateseparation. For example, the lumen may define a portion of aMobius-strip-like structure, having an axis that includes at least 180°of axial twist along the flow path. This axial twisting (often againwith an elongate lumen cross-section) may be defined by channels in astack of plates, by twisting a flexible conduit about it axis, or thelike. The fluid path will preferably comprise a laminar fluid path, andthe port will be included within a bifurcation having an acute anglebetween the target matter flow path (along a target matter lumen) andthe fluid flow path.

The conduit will often comprise a material having an acoustic impedancethat sufficiently matches an impedance of the fluid flow to inhibitreflection of the waves when the waves from the biological fluid impingeon the conduit. For example, the conduit material may have a Raylesnumber that is within about 15% of the Rayles number of the biologicalfluid, ideally being within about 10% of the Rayles number of thebiological fluid. Where the biological fluid comprises blood, suitablematerials for including in the conduit may have an acoustic impedance ofbetween about 1.2 MRayle and 1.7 MRayle, with exemplary materialscomprising an ultrasound probe head material, a polymethyl pentane suchas TPx (which may be commercially available from Mitsubishi Corp. ofJapan), HDPE, or UHDPE. Reflection of the waves may also be inhibited bycontrolling the angle at which the waves from the biological fluidstrike the conduit, with exemplary embodiments having waves striking theconduit at close to about 90°, such as between about 80 and 110°.

The transmitter may be attached to a structure having a receptacle whichremovably receives the conduit, and which maintains acoustical couplingbetween the transmitter and conduit. While some embodiments may employ afluid bath encompassing the conduit and at least a portion of thetransmitter and/or openings in the conduit to directly expose thetransducer surface to the fluid flow, exemplary embodiments may rely onsimple engagement between a flexible conduit material and the transducersurface to facilitate removal and replacement of the conduit so as toavoid cross-contamination of sequential fluid flows and decrease theneed for costly sterilization. Such coupling may optionally be enhancedby a gel at the interface between the transmitter and the conduitmaterial.

While a variety of standard wave forms might be employed to sweep thetarget matter from the stream of fluid, exemplary embodiments may employnon-standard complex waveforms to drive the transmitter. For example,rather than a simple standard sign wave, a square wave, a triangularwave, or the like, tailored waveforms having multiple changes incurvature (such as a waveform that undergoes a plurality of changesbetween a positive second derivative and a negative second derivative)as the wave advances between a minimum and maximum amplitude within asingle cycle. Waveforms generated by a less than 25% duty cycle (such asa waveform generated by a 10% duty cycle) may also be employed. Varyingor sweeping of the ultrasound frequency may also be employed to inhibitthe formation and/or deleterious effects of standing waves.

The target matter may comprise gas bubbles such as microbubbles or thelike, and the fluid flow may comprise blood flow. Alternativeembodiments may filter microspheres, polymer or other beads, or the likefrom biological or other fluids, and/or may manipulate these targettissues within biological or other fluids.

In another aspect, the invention provides a method for filtering abiological fluid. The method comprises flowing the fluid along a fluidflow path. Target matter is driven from within the flowing fluid towardsa target matter port by directing ultrasound or acoustic waves acrossthe fluid flow path. The target matter is removed from the fluid flowpath through the port.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a cardiopulmonary bypass systemincluding an embodiment of a filter of the present invention.

FIG. 2 is a side view showing an exemplary filter for the system of FIG.1.

FIG. 3 is a cross-sectional view within the filter of FIG. 2, showinggravity-assisted ultrasound waves driving microbubbles upward within aconduit from a blood flow path.

FIG. 4 is a side view of an alternative embodiment of a biological fluidfilter for use in the system of FIG. 1.

FIGS. 4A and 4B are a prospective view and end view, respectively, ofthe filter conduit structure of the filter of FIG. 4.

FIGS. 4C through 4G are side views showing the structures of plates thatcan be stacked together to form the filter of FIG. 4.

FIG. 5 schematically illustrates a complex waveform having a pluralityof changes in curvature sign between adjacent maximum and minimumamplitudes.

FIG. 5A schematically illustrates an alternative waveform having a 10%energized pulse duty cycle for driving the ultrasound transducer.

FIG. 6 schematically illustrates sweeping the driving frequency of thetransducer so as to inhibit the formation of standing waves within thefiltering conduit.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides improved devices, systems, andmethods for manipulating target materials within fluids and/orseparating those target materials from fluids. Advantageous embodimentsallow filtration of acoustically manipulatable or low-density materials(such as bubbles, microbubbles, microspheres, beads, microbeads, and/orthe like) from blood or other biological fluids. Exemplary embodimentsuse acoustic or ultrasound waves to drive microbubbles across a flow ofblood within a conduit and towards a target matter removal port. Hence,aspects of the invention may have applications for removing gaseousbubbles or microparticulates during cardiopulmonary bypass, dialysistreatments, cell savers blood scavenging and separation for return tothe patient during surgery, as a supplemental system for catheters,during femoral artery to femoral artery (sometimes referred to as“fem-fem”) bypass procedures, during known or newly developed bloodfiltration (including custom filtration) treatments, and the like.Additional embodiments may be used for filtration of other fluids,including medications or the like. Still further alternative embodimentsmay be used during filtration of other fluids, such as removal ofmicrobubbles from industrial fluids.

Referring now to FIG. 1, an exemplary cardiopulmonary bypass system 10may include a heart-lung machine 12 for pumping and oxygenation of bloodfrom a patient P. Blood from the patient P enters the heart-lungmachine, which generally operates under the control of a controller 14.As a result of the processing of the blood within heart-lung machine 12,the blood leaving the heart-lunch machine may include gaseousmicrobubbles and/or other embolized microparticulates.

Before the blood from heart-lung machine 12 is reintroduced into patientP, the blood passes through a filter 16. Filter 16 generally makes useof acoustic or ultrasound waves to drive microbubbles and/orparticulates across a flow of the blood toward a target matter removalport, with the waves being generated by a transmitter energized by adriver 18 under the control of controller 14. While schematically shownin FIG. 1 as being separate from heart-lung machine 12, filter 16 may beincorporated into heart-lung machine 12 of cardiopulmonary bypass system10. Alternatively, the individual components of heart-lung machine 12may be separated into a variety of alternative fluid path structures.Optionally, a sensor 20 determines the efficacy of filter 16 and/orcardiopulmonary bypass system 10, providing feedback signals to theprocessor 14 of the system.

Processor 14 will typically comprise digital and/or analog dataprocessing circuitry, often including the electronic hardware and/orcomputer programming software. Suitable hardware may include a generalpurpose personal computer, workstation, or the like, or may include aspecialized proprietary processor or processor board. The hardware ofprocessor 14 will often be combined with software in the form ofmachine-readable programming instructions or code for implementing one,some, or all of the methods described herein. The code will often beembodied in a tangible media such as a memory, a magnetic recordingmedia, an optical recording media 22, or the like, and/or may betransmitted to processor 14 as electrical signals, optical signals,wireless data signals, or the like. Data and code transmission may beimplemented via a cable, an Intranet, an Internet, a wireless network,or the like. Processor 14 will often have or be coupled to appropriateinput and output devices for communications between the processor andthe user, such as a keyboard, mouse, touchscreen display or other userinterface for communications with a user of cardiopulmonary bypasssystem 10.

Referring now to FIG. 2, an exemplary filter 16 includes a conduit 28held in place relative to an ultrasound transmitter 30 by a supportstructure 32. Conduit 28 includes an input end 34 coupled to an outputend 36 by a lumen 38. Blood flows into input end 34 from heart-lungmachine 12, and flows out from output end 36 toward the patient P. Theinput and output ends may include couplers such as Luer fittings or thelike. Conduit 28 may comprise any of a wide range of polymer or othermaterials, with lumen 38 optionally having one or more coatings toinhibit deleterious interaction between the bloodstream and thesurrounding conduit material. Conduit 28 may, for example, comprise acast, molded, or extruded TPx, high-density polyurethane, or ultra highdensity polyurethane.

Exemplary conduit 28 shown in FIG. 2 has a form that is described hereinas resembling a portion of a Mobius strip. In general, the lumen withinconduit 28 will promote laminar flow of the bloodstream, at leastadjacent ultrasound transmitter 30. Such laminar flow can be promoted ina variety of different ways, such as by providing appropriate luminalsurface shapes for the Reynolds number of the blood flow that will passtherethrough by providing sufficiently smooth luminal surfaces,transitions, and the like. The lumen adjacent transmitter 30 willtypically have a height H which is significantly greater than theluminal width, the height typically being at least two times the luminalwidth, often being at least four times the luminal width at thetransmitter. The exemplary Mobius filter structure has an axial twist ofabout 90° between the inlet end 34 and transmitter 30, and another axialtwist of about 90° between transmitter 30 and the output end 36. Thiscan help balance the flow resistance across the lumen. Also, filter 28will often be positioned so that an upward orientation 40 of the lumenadjacent transmitter 30 helps urge microbubbles toward a target filtermatter port and associated target matter lumen 42. By sufficientlyaligning the direction of the applied acoustic force upon the targetmatter with the direction of the buoyant force on the target matter,separation can be enhanced. Gravity forces on the target material may beopposed to the buoyant force, and both drag and flow may be at leastpartially perpendicular to the buoyant force. The exemplary Mobiusfilter has an upper luminal surface that slopes upward prior to adjacenttransmitter 30, and then slopes downward after transmitter 30 (as can beunderstood with reference to FIGS. 2 and 3). Alternative conduit shapes,cross sections, and flow paths may also be used, including non-twisting,locally peaking channels.

In operation, the waves directed from transmitter 30 drive microbubbles54 upward and toward a target matter port 44 for extraction from lumen38 via a target matter lumen 42. Ultrasound transmitter 30 may compriseany of a wide variety of commercially available ultrasound transmittingstructures, including transducers having transmitting and receivingcapabilities. One exemplary transmitter comprises a 1″ diameter(optionally having a 2″ diameter) ceramic ultrasound transducercommercially available from Channel Industries, Inc. of Santa Barbara,Calif. under the model name Navy III™ 5800 PZT 1 MHz transducer. Thisexemplary transducer may, for example, transmit ultrasound waves at 1MHz or less, with the effective size of the transmitting surface oftenbeing less than the overall transducer size (the primary mode of thetransducer often comprising about the center ⅔rds of the overalltransducer radius). One MHz ultrasound energy may have a wavelength ofabout 1.4 mm in blood, with lower wavelengths generally providing betterfiltering performance. Driving such a transducer at lower frequencies,such as at about 580 kHz, may improve filtering effect, while altering,varying, and/or sweeping the driving frequency can inhibit standingwaves and improve the overall capabilities of the filter. Relativelylarge transmitting surfaces may transmit waves more uniformly acrosslumen 38, inhibiting deleterious reflection of the waves by limiting anangle at which the waves propagating through the lumen strike theluminal wall of conduit 28. Deleterious reflection of the waves may alsobe inhibited by sufficiently matching acoustic impedance of the conduitmaterial to that of the fluid within in the lumen. For example, suitablematerials for a blood filtering may have an acoustic impedance in arange of from numbers of about 1.2 MRayle to about 1.7 MRayle.

A variety of structures and approaches may be employed to provideacoustic coupling between transmitter 30 and the blood flow withinconduit 28. In the exemplary embodiment, support 32 includes a pluralityof arms 46 that hold conduit 28 in position with the conduitacoustically coupled to transmitter 30. Advantageously, arms 46 ofsupport structure 32 may replaceably hold conduit 28 in acousticengagement with transmitter 30. Specifically, inner surfaces of the arms46 may each define receptacles, with the receptacles togethersufficiently supporting and positioning the conduit for use. Removal andreplacement of conduit 28 between treatment of different patients mayhelp avoid cross-contamination. Arms 46 may be, for example, movablerelative to the conduit to facilitate replacement of conduit 28 with adifferent conduit for treatment of another patient. In otherembodiments, the conduit may deform sufficiently to be held by detentsof the arms, the arms being fixed. A wide variety of alternativereceptacle surface structures might also be employed, includingstructures which support the conduit using fasteners (such as threadedfasteners or the like) latches, or the like. Optionally, a fluid tanksimilar to that described in U.S. Pat. No. 5,344,136, the fulldisclosure of which is incorporated herein by reference, may enhanceacoustic coupling by including at least a portion of the transducersurface and conduit in a fluid bath, although such coupling may insteadbe accomplished without a fluid bath by direct engagement betweenconduit 28 and transducer 30, by a gel at the conduit/transducerinterface, or the like.

Removal of microbubbles from the bloodstream within conduit 28 can beunderstood with reference to FIGS. 2 and 3. Waves 50 propagate throughlaminar flow 52 of the blood through lumen 38. Aided by gravity, waves50 drive microbubbles 54 upward across the flow within lumen 38. Drawingthe target matter through target matter lumen 42 with a speed sufficientto roughly matching the flow velocities at the entrance of the targetmatter lumen with that of the flow in lumen 38 may help maintain laminarflow adjacent target matter port 44. Laminar flow may also be maintainedby providing a relatively narrow bifurcation angle adjacent port 44between the target matter lumen 42 and lumen 38. Sufficient smoothing ofthe bifurcation and the like may also help maintain the smooth laminarflow. The blood (or other fluid) continues to flow as it is beingfiltered, and the filtering by waves 50 does not expose the blood flowto a large filter media surface area that might add to microparticulateembolization, generate additional microbubbles, or the like.

Microbubbles 54 tend to collect between peaks of waves 50, so that themicrobubbles may be moved laterally across the bloodflow path as thewaves propagate. The wavelength and power of waves transmitted bytransmitter 30 will preferably be sufficiently low to avoid cavitationor damage to the blood, and specific power and wavelengths for aparticular conduit may be determined by appropriate parametric studies.Typical filters will have powers of from about 20 to about 50 W, withfrequencies of from about 400 kHz to about 4.5 MHz. Transducers capableof handling 250 watts at 15 volts rms (or greater, optionally being 100volts rms) and 10 amps may be suitable for some embodiments. Including asuitable material in the conduit where the waves strike the luminal wallcan inhibit reflections, as can maintaining the angle between theimpinging waves and the luminal surface sufficiently close to about 90°.

An alternative filter 60 can be understood with reference to FIGS. 4 and4A through 4G. Filter 60 again includes a conduit with a lumen providingfluid communication between an input 62 and an output 64. In thisembodiment, the conduit comprises a series of plates having channelstherein, with the channels together defining a lumen 66 when the platesare stacked together. Lumen 66 once again follows a path 68 similar inform to Mobius strip, with the luminal walls presenting an elongate,relatively thin cross-section adjacent transmitter 30.

The lumen path 68 within filter 60 can be understood by reviewing theindividual channels of the plates from which the conduit is formed (seeFIGS. 4C-4G), and by comparing those channels to the side, end, andperspective view of FIGS. 4, 4B and 4A, respectively. The conduit offilter 60 includes three plates 72, 74 positioned between two end plates78, 80. Central plate 74 may also define the target matter lumen 82 andport 84. An opening 86 in each of the plates accommodates ultrasoundtransmitter 30. As can be seen in FIG. 4A, ultrasound transmitter 30 mayoptionally be acoustically coupled to the flow within the lumen byproviding an opening in the conduit.

Referring now to FIG. 5, the general characteristics of a waveform whichmay enhance filtering efficacy when applied by driver 18 to theultrasound transmitter of filter 16 (see FIG. 1) is schematicallyillustrated. The curvature of waveform 90 varies between a positivecurvature (second derivative of greater than 0) and a negative curvature(second derivative of less than 0) a plurality of times within a singlecycle between a maximum amplitude 92 and a minimum amplitude 94. Analternative waveform which may enhance filtering efficacy is illustratedin FIG. 5A, with the waveform here having a 10% duty cycle. Sign waves,square waves, triangular waves, and other standard shapes may be used insome embodiments, but not provide the same microbubble filteringefficacy, even though waveform 90 may be generated without providingtrue resonance in the driving circuit as is typically desired for powercircuits.

Referring now to FIG. 6, driving the transducer with a frequency f whichchanges over time may inhibit the formation of standing waves. Suchstanding waves might otherwise interfere with filtering of target matterfrom the fluid flow. A variety of changes, alterations, or variations tothe frequency might be employed, with the exemplary sweeping of thefrequency comprising a smooth and gradual change from about 50 kHz belowan optimized or desired filtering frequency Opt to about 50 kHz abovethe optimized or desired filtering frequency. Each sweep may takebetween about 0.01 sec and about 50 sec. Incremental changes infrequency might also be employed in other embodiments.

While the exemplary embodiments have been described in some detail, byway of example and for clarity of understanding, those of skill in theart will recognize that a variety of modification, adaptations, andchanges may be employed. For example, multiple ultrasound filter stagesmay be used to decrease blood or other filtered fluid loss. High densitytarget materials might be filtered from lower density fluids usinggravity assistance by positioning the target material port below thelumen. A wide variety of other changes might similarly be made. Hence,the scope of the present invention should be limited solely by theappending claims.

1. A filter for separating a target matter from a fluid flow, the filtercomprising: a fluid conduit having an input for receiving the fluidflow, an output, and a lumen defining a fluid flow path from the inputto the output; an ultrasound or acoustic transmitter for transmittingultrasound or acoustic waves; and a target matter port in fluidcommunication with the conduit lumen, the transmitter oriented so thatthe waves drive the target matter across the fluid flow path toward theport.
 2. The filter of claim 1, the fluid flow at the input comprisingthe target matter and a biological fluid, the target matter being lessdense than the fluid, wherein transmitter is disposed below the fluidflow path and the port is disposed above the fluid flow path.
 3. Thefilter of claim 2, wherein the fluid conduit has an upper surface, theupper surface sloping, along the fluid flow path, upward toward the portand then downward away from the port.
 4. The filter of claim 3, whereinfluid path resistance across the lumen is balanced.
 5. The filter ofclaim 4, wherein the lumen defines an axis and at least 180 degrees ofaxial twist along the flow path.
 6. The filter of claim 4, wherein theconduit comprises a first body, a second body, and a third body, eachbody having a channel and sandwiched between a first end plate and asecond end plate, the channels together defining the lumen; the channelof the second body defining the upper surface and at least a portion ofa target matter lumen; the first body disposed between the second bodyand the first end plate, the channel of the first body coupling theinput to the channel of the second body with a 90 degree twisttherebetween; the third body disposed between the second body and thesecond end plate, the channel of the third body coupling the channel ofthe second body to the output with a 90 degree twist therebetween. 7.The filter of claim 4, wherein axial twist extends along a significantlength of the lumen.
 8. The filter of claim 1, wherein the fluid pathcomprises a laminar fluid path.
 9. The filter of claim 8, wherein abifurcation couples a target matter lumen to the lumen at the port, thebifurcation having an acute bifurcation angle.
 10. The filter of claim1, wherein the conduit comprises a material having an acoustic impedancesufficiently matching an impedance of the fluid flow to inhibitreflection of the waves.
 11. The filter of claim 1, wherein thetransmitter is oriented so that the ultrasound waves impinge on a lumenwall of the conduit at an angle so as to inhibit reflection of thewaves.
 12. The filter of claim 1, wherein the transmitter is attached toa structure having a receptacle, the receptacle removably receiving theconduit so that the transmitter is acoustically coupled to the lumen.13. The filter of claim 1, further comprising a power source coupled tothe transducer, the power source applying an alternating waveform to thetransducer, the waveform having a curvature with a plurality of changesin sign between a maximum amplitude of the waveform and an adjacentminimum amplitude of the waveform.
 14. The filter of claim 1, furthercomprising a power source coupled to the transducer, the power sourceapplying a waveform to the transducer, the waveform having a frequencythat varies during driving of the target matter with the waves.
 15. Thefilter of claim 1, wherein the target matter comprises gas bubbles andthe fluid flow comprises blood flow.
 16. The filter of claim 1, whereinthe lumen has an elongate cross section with a first cross sectionaldimension between adjacent the transmitter and adjacent the targetmatter lumen, and a second smaller cross sectional dimension transverseto the first cross sectional dimension.